Induction heating method and means



Nov. 10, 1964 J. A. STEIN ETAL 3,156,807

INDUCTION HEATING METHOD AND MEANS Filed Oct 27, 1961 8 Sheets-Sheet 1 INVENTORS JOHN A. STEIN y THERIAN E. AUSTIN NN N ATTORNEY Nov. 10, 1964 J. A. STEIN ETAL INDUCTION HEATING METHOD AND MEANS 8 Sheets-Sheet 2 Filed Oct. 27, 1961 INVENTORS JOHN A. STEIN BY THERIAN E. AUSTIN ATTORNEY Nov. 10, 1964 J. A. STEIN ETAL INDUCTION HEATING METHOD AND MEANS 8 Sheets-Sheet 3 Filed Oct. 27, 1961 6 o 2 2 M 8 D P ill w 8 6 7 6 2 M I 6, 5 m 7 Q 111.. w\ ll.l\|.l|l||.l|.l| z n O 2 I 1 1 04 x 3 4 2 T f x x 2 5 I I M v,/ z r O O r I? ll 2 m i 2 s 4 H 0 2 w Mm 7 7 .l w. m I 6 n U 9 O l| W 2 8 4 2 o u H m 8 m l IEJE'IIE 1 INVENTORS JOHN A. STEIN By THERIAN E. AUSTIN \& ATTORNEY FIG. 5

Nov. 10, 1964 J. A. STEIN ETAL 3,156,807

INDUCTION HEATING METHOD AND MEANS Filed Oct. 27, 1961 8 Sheets-Sheet 4 INVENTORS JOHN A. STEIN BY THERIAN E. AUSTIN NNK P ATTORNEY Nov. 10, 1964 J. A. STEIN ETAL 3,156,307

INDUCTION HEATING wz'mon AND MEANS Filed Oct. 27, 1961 8 Sheets-Sheet 6 INVENTORS JOHN A. STEIN By THERIAN E. AUSTlN ATTORNEY 8 Sheets-Sheet '7 INVENTORS JOHN A. STE I N THERIAN E. AUSTIN am -w ATTORNEY Nov. 10, 1964 J. A. STEIN ETAL INDUCTION HEATING METHOD AND MEANS Filed om. 27, 1961 FIG. I4

Nov. 10, 1964 J. A. STEIN ETAL 3,156,807

INDUCTION HEATING METHOD AND MEANS Filed Oct. 27, 1961 8 Sheets-Sheet s Zea g RELAY FIG. l6

INVENTORS JOHN A. STEIN BY THERIAN E. AUSTIN ATTORNEY United States Patent Inc.

Filed Oct. 27, 1961, Ser. No. 148,171 4 Claims. (Cl. 219-95) This invention relates to method and means for applying heat to a workpiece as required for various manufacturing or repairing operations thereon, including localized heat treatment of parts, and the formation of brazed conduit joints and connections. More particularly, the invention contemplates improved method and means for applying heat in precise predetermined amount for accurately controlled periods of time to workpieces such as required for in-place brazing of steel tubing in crowded installations.

Although the invention is of wide applicability in forming a variety of diverse joints o-r connections between elements of difierent forms and materials for various purposes, it will be described for the sake of illustration in connection with high strength tubes or conduits used in aircraft and high speed aerial or space vehicles. It will be understood that the scope of the inventive concept is in no sense limited by any of the specific details used to explain the invention, except as determined by reference to the accompanying claims.

Modern aircraft and aerial vehicles, whether manned or not, are characterized by a high degree of complem'ty which, combined with the need for efiicient use of all available space, results in extremely crowded internal conditions. Tubes and conduits such as required for hydraulic lines or other systems in the stated environment are usually formed in separate sections of various shapes as required to route them through compartments and bulkheads. The abutting ends of adjacent conduit sections must be aligned and secured to each other by means which will maintain the continuity of flow within the conduit or tube and prevent leakage at the joint formed between the sections. The stated joints are required to be of great strength inasmuch as fluid conduits in vehicles of the stated type are normally affixed to the vehicle frame and are therefore affected both by vibrations and by deflections in the frame such as would tend to loosen, distort or otherwise adversely affect the the alignment of the separate conduit sections, the structure used to maintain such alignment, or leakage properties of the joints. Defiections of the fuselage and Wing structure in vehicles of the type mentioned above are frequently encountered due to aerodynamic and inertia loads imposed on the vehicles during their operation.

The choice of method and means for securing adjacent conduit ontube sections of the stated type is further influenced by the need for minimum size and weight of structural components for use in ultra-high speed aerial and space vehicles. Moreover, flow systems involving extreme fluid temperature and stress conditions such as 4000 psi. and 500 F. require use of materials of construction formely unknown in the fabrication of conventional supersonic aircraft. Notable among such materials are the so-called advanced alloys of precipitation hardenable stainless steel, of which the alloy designated as 350 stainless steel is illustrative. The component elements and general range of percentage composition by Weight for 350 stainless steel is as follows:

Percent Carbon 0.08-0.12. Manganese 0.75-1.24. Silicon 0.50 \Phosphorus 0.04 maximum. Sulfur 0.03 maximum. Chromium 16.00-17.00. Nickel 0.00-5.00. Molybdenum 2.50-3.25. Nitrogen 0.07-0.13.

While the stated precipitation hardenable alloys including 350 stainl ss steel provide great strength at extreme environmental temperatures when used in fluid conduits or tubing, such materials are characterized by a reduction in strength when heated excessively. Thus, for example, during a brazing operation to join workpiece materiais of precipitation hardenable stainless steel in the hardened condition, the application of heat in an amount sufixcient to melt the brazing alloy may cause annealing and consequent weaking of the conduit material in the absence of measures to control the intensity, the duration, and the area of application of such heat.

In connection with the particular sensitivity of precipitation hardenable stainless steels to the application of brazing heat, new brazing alloys have been recently developed for use in the problem situation discussed herein, in order to minimize the amount and duration of brazing heat. Moreover, resort to improved power supply connections has been necessary because conventional power sources and connections lack the ability to create sufficient heat for induction brazing involving the materials and alloys discussed above at locations relatively distant from the power source, as required for in-place brazing.

Accordingly, it is a principal object of this invention to provide improved connection method and means for securing adjacent separate sections of tubular conduits or the like to each other at the adjoining end thereof.

It is a further object of this invention to provide improved connection rnethod and means as set forth in these objects suitable for use in an environment characterized by high pressure, high temperature, and vibration of diverse frequencies and amplitudes for prolonged periods.

It is a further object of this invention to provide an improved conduit connection as set forth in these objects characterized by superior strength and performance reliability.

It is another object in this case to provide a conduit connection as set forth in these objects which is capable of installation in crowded equipment areas providing severely limited Working space around the stated connection.

It is also an object of this invention to provide conduit connection method and means as set forth in these objects characterized by accurate and automatic temperature controls.

It is an additional object in the instant case to provide induction heating means for brazing a connection a set forth in the above objects when such connection is situated at great distances from the power source for causing such heating.

Other objects and advantages of the instant invention will become apparent upon a close reading of the following detailed description of an illustrative embodiment of the invention, reference being had to the accompanying drawings, wherein:

FIGURE 1 shows a general perspective overall view of system components adapted to accomplish in-place brazing in an aerial vehicle according to the inventive principles disclosed herein,

FIGURE 2 is an isolated perspective view of the brazing fixture shown by FIGURE 1 on a larger scale,

FIGURE 3 is a fragmentary view in cross-section taken along line 33 of FIGURE 2, with portions of structure omitted for the sake of clarity,

FIGURE 4 is a cross-sectional view taken on a vertical plane through the center of the brazing fixture shown by FIGURES 1 and 2,

FIGURE 5 is a plan view taken through the plane of separation between the two halves of the brazing fixture shown by FIGURES 1, 2 and 4, looking downwardly upon the lower half thereof,

FIGURE 6 is an exploded view in perspective of the brazing fixture shown by FIGURES 1-5, inclusive,

FIGURE 7 is a side elevational view of the induction coils forming part of the brazing fixture shown by FIG- URES 1-6, inclusive,

FIGURE 8 shows a cross-sectional view taken on a vertical plane through the center of the structure shown by FIGURE 7, including in addition thereto, a fragmentary view of a cable end adapted for connection with the stated coil, while FIGURE 8a is a variation in certain details of FIGURE 8,

FIGURE 9 is a fragmentary view showing details of the separable connection means between upper and lower portions of the spread induction coil of FIGURES 7 and FIGURE 10 is an isolated view in perspective showing the general relationship between parts in a magnetic element for controlling duration of the application of brazing heat by the fixture shown in FIGURES 1 through 9, inclusive,

FIGURE 11 i a cross-sectional view throngs a portion of structure which may form part of the induction coil shown by FIGURES 1 through 9, inclusive, incorporating the temperature control means shown by FIGURE 10,

FIGURE 12 is a partial cross-sectional view of a power cable connector adapted for use with the brazing coil of FIGURES 7-9, inclusive,

FIGURE 13 is a cross-sectional view taken along line 13 113 of FIGURE 12,

FIGURE 14 is a partial cross-sectional view of the cable connector of FIGURE 12 taken on a plane at right angles to the view shown by FIGURE 12,

FIGURE 15 is an elevational view, partly in section, of a modification of the cable connector shown by FIG- URES 1214, inclusive, and

FIGURE 16 is a schema-tic view showing the general circuitry and the relationship between the electrical and the pneumatic portions of the brazing system of FIG- URE 1.

With reference to the drawings described above, and particularly to FIGURE 1, the invention disclosed herein may be seen to include a brazing fixture generally designated by reference numeral It shown operatively positioned to form a joint or connection between two adjacent structural elements in the form of metallic conduit sections 12 and 14 Within a missile or aerial vehicle I6. Although the structure surrounding conduit sections 12 and 14 is not shown in FIGURE 1, it will be understood that the total volume within vehicle 16 may be characterized by extremely crowded conditions which severely limit the working space available. Accordingly, brazing fixture In is preferably of small and compact nature, and is adapted to receive all of its operating requirements through cable means 18 whereby the power generator or transformer means for furnishing such requirements may be situated remotely from the precise locations at which brazing is accomplished by fixture Ill. Such remote location of a brazing fixture relative to its power source is not necessary in the case of bench brazing where no problem of limited access normally exists. Since power generator 2'?) and transformer 22 are standard commercially available items for supplying electrical impulses at diverse amplitudes and frequencies as required for welding or brazing operations, the details thereof need not be shown in the instant case and form no part of the concept herein.

As shown in greater detail by FIGURE 2, brazing fixture Ill comprises in general an annular housing divided into two separable portions 24 and 25 which contact each other on a plane of separation 28. Two aligning stakes or pins 23 and 25 on portion 26 enter holes 27 and 29 in portion 24 to insure correct positioning of the two stated housing portions in operative relationship, while holding means in the form of threaded studs 31, 33, and 37 apply tension between portions 24 and 26 to maintain the stated relationship asshown by FIGURE 6. Brazing fixture It further comprises induction heating means in the form of coil element 349 comprising separable portions 32 and 34 of dielectric material as shown more particularly by FIGURE 7. Clamping means such as shown by reference numeral 36 in FIGURE 2 situated on either side of annular housing portion 24 serve to retain coil element 3b in operative relationship with annular housing portions 24 and 26.

Position adjusting means for altering the relative position between coil element 30 and annular housing portion 24 are provided in brazing fixture Iii in the form of two adjusting screws 38 and 4b as shown by FIGURE 3. Thus, the position of coil element 39 within annular housing portion 24 may be varied with respect to the same in a direction coinciding with the longitudinal axis of conduit sections 12 and 14 by rotation of adjusting screws 38 and 40, the distal ends of which bear against opposite sides of the coil element.

The operative relationship between brazing fixture 10 and the workpiece components upon which'the brazing operation is accomplished may be seen from FIGURE 4 which shows adjacent conduit sections I2 and 114 in substantial axial alignment with their ends contacting in a plane of abutment 42 centrally located within a brazing sleeve or bushing 44 about which brazing fixture Ill is secured. Fixture It) in essence combines induction heating means for heating the assembled workpiece compoents to 'braze the same, cooling means for cooling the induction heating means, purging means to provide an inert atmosphere around the brazing area, aligning means to insure proper relationship between fixture Ill and the assembled workpiece components, and temperature control means to limit the duration or amount of applied brazing heat. Each of the foregoing essential features of fixture I0 is operatively interrelated with the remain ing features as discussed below in the foregoing order following which the novel power supply means for connecting fixture III to a remotely located power source is described.

Induction heating means as referred to above is provided in the form of one or more hollow rings 46 of electrically conductive materials embedded within a suitable high temperature resistant dielcctric mass 32, 34, which, together with the stated ring or rings, comprises coil element 34). Rings 46, whether one or several, form in effect a single continuous hollow tube which begins at 43 as shown in FIGURE 4 and winds in spiral turns culminating in tube end whereby a flow of current originating from a source connected at 4% may be transmitted through the tube walls and return to the stated source through 50. Cooling air outlet means in the form of apertures 52 are provided at a peripheral location on each ring as remote from the connection of rings to with portions 48 and 50 whereby cooling air introduced through 48 and t may flow through the hollow center of the tube and exit through the stated apertures.

Due to the separable nature of coil 39 into two portions 32 and 34 as described above, rings 46 are formed by two portions 47 and 49 contacting each other on plane of separation 2d. Coil coupling means generally designated by reference numeral 39 in FIGURE 7 are provided so that electrical and fluid flow continuity will result in the coil formed by rings 46 when portions 32 and 34 are assembled in operative relationship. Coupling means 39 is shown in greater detail in FIGURE 9 wherein it may be seen that upper ring portion 47 terminates in an aperture formed by the walls or" ring which may be generally of square configuration as seen, for example, by the sectional view therethrough in FIGURE 8. FIG- URE 9 also shows bushing or sleeve means for insertion in the terminal aperture of ring portion 47, the stated means comprising hollow bushing member 51 which may be welded, brazed or otherwise secured within lower ring portion as indicated at 53. in addition to electrical contact between upper and lower ring portions 47 and 49 through plug member 51, electrical continuity across coil coupling 39 is also insured by the provision of two cooperating blade electrodes and 57 adapted to contact each other over a substantial portion of their confronting surface areas as seen in FIGURE 9. Thus, electrode '7 may be integrally formed or otherwise socured to lower ring portion 4? in the area indicated by reference numeral 59 whereby blade portion 57 is socured in spaced relationship from ring portion 49 as shown by FEGURE 9. Electrode 55 may be formed by a strip of metal secured to upper ring portion 47 whereby a downwardly depending portion 61 of electrode 55 is aligned and clamped within space or gap 63 formed by the spaced relationship of electrode 57 and lower ring portion as described above.

Purging means, as mentioned above, are included in fixture it) in the form of an annular chamber 54 defined in part by cylindrical wall 56 which may be fabricated from lyrex glass or suitable ceramic material. Wall 56 comprises two arcuate portions 53 and 6%) which contact each other on plane of separation 2%. Portion 53 is mounted within annular housing portion 24 by means of arcuate grooves 62, and 64 at either end thereof. Arcuate portion is mounted within annular housing portion 26 by means of arcuate grooves es and es at either end thereof, as shown, for example, by FIGURES 4 and 6. Additional grooves are provided as shown in FIGURES 4 and 6 to accommodate arcuate sealing means 65 and d7 which are high temperature resistant material having suitable scaling properties to prevent leakage of purging gas from chamber $4 at either end of arcuate portions 58 d9. Moreover, member 65 aids in confining the electro-magnetic heating eilects of coil element 3b to the general area of bushing Referring again to FIGURE 4, it may be seen that chamber 54 is further defined by inner surfaces ill and '72 of annular housing portion inner surfaces '74 and of housing portion 26, and scaling or annular bearing eans 734%4 at either end of chamber 54 which seal the some from the surrounding atmosphere. The stated annular bearing means comprises arcuate bearing members 73 and till mounted in housing portion 2%, and arcuate bearing members $23 and 84 mounted in housing portion 26 whereby members 73 and 82 contact each other on the plane of separation 23 to form a seal at one end of chamber 5d, and members $49 and 34 similarly contact each other at the other end of the stated chamber, as seen, for example, in FIGURES 4 and 6.

in further connection with the purging means as referred to above, arcuate bearing members 78, 8d, 82 and 84 each comprise in essence a cylindrical midportion with flanges at each end as shown more particularly by PIG- URE 6. Thus, for example, bearing member 78 comprises cylindrical portion 536 having inwardly directed flanges 88 and 9d at either end thereof, and outwardly directed flange 92 for attachment of bearing member 78 to housing portion 24- by appropriate means such as a plurality of screws (not shown) which may pass through one or more holes 94 spaced as necessary around flange 2. inwardly directed flanges 8d and tl on member 78 are adapted to bear against the outer surrace of a workpiece component such as conduit section 12 as shown in FIGURE 4, for example. In a similar manner, contact of the inwardly directed flanges on the other bearing members 8%, 82 and S4 with conduit sections 12 and 14 functionally cooperate to form sealing means at each end of chamber 54.

The purging means to which reference is made above further includes conduit means 96 and 98 connected to passage means int) and 1%, respectively, as shown in FlGURE 4, for example. A suitable inerting agent such as argon gas may be supplied to chamber 54 through con-' duit means and passage res, while passage 102 and conduit 98 may provide a path for exit flow of the purging agent.

Aligning means as mentioned above are included in fixture It to insure proper operative relationship between the fixture and assembled workpiece components upon which the brazing operation is performed. The stated aligning means may be seen from FIGURE 6, for example, to include pins 1M and res mounted on arcuate bearing members 78 and 8d, respectively. With the stated bearing members affixed to housing portion 24, and the stated aligning pins immovably secured to members 78 and 30, it will be seen from FIGURE 5, for example, that contact or" the distal end of each stated pin with the 0pposite ends of sleeve or bushing 44 will result in alignment of fixture It? with respect to bushing 44 in precisely the same relationship each time that the fixture is employed to braze a bushing of the particular size adapted for use with a given fixture. In consequence of the alignment of fixture It? by means of pins EM and 1% as discussed above, it will be understood that alignment of coil element 3% with respect to bushing 44 automatically occurs by reason of the relationship between coil element 3%) and fixture it) as determined by rotational adjustment of screws 33 and 4d discussed above and shown in FIG- URE 3.

Temperature control means as mentioned above are included in fixture lit to limit the duration or amount of applied brazing heat and may be seen from FIGURE 4, for example, to include circuit interrupting means in the form of pivotally movable member 168 which is mounted on housing portion 26 of fixture 18 by pivot means at 118. in the embodiment shown by FIGURE 4, member 1818 comprises a bar magnet having a bearing portion 112 at one pole thereof adapted to contact the surface of conduit section 12. At the end of member 138 opposite from bearing portion 112, means are provided for the application of force to the member tending to rotate it counterclockwise as seen in FlGURE 4. The stated force means may take the form of a resilient member such as spring 114 which bears against a flange 116 tending to move a spring guide 113 to which the flange is attached whereby downward force is transmitted from spring 114 to one end of member Hi8 which is contacted by the lower end of spring guide 118. The end of spring 114- opposite from that which contacts flange 11d bears against a threaded plug 12% operatively engaged within a hole 122 in closing portion 26 whereby rotation of plug 129 moves the same vertically to adjust the force of compression spring 114.

FIGURE 10 shows temperature control means constituting a slightly dii'lerent modification of the structure discussed above in connection with FIGURE 4. Thus, it may be seen from FEGURE 10 that pivotally movable member 124 may be non-metallic, and is provided with a small magnet 126 having a surface 123 which may be of curved contour conforming to the surface shape areas ,3, of conduit section 12 and adapted to contact the same. Pivot means to permit rotational movement of member 124 within a limited range are provided in the form of threaded screws 13% and 132 operatively engaged within relatively stationary blocks 134i and 136, respectively, and provided with low-friction bearing points such as shown at 138 adapted to engage member 124 on either side thereof to provide a pivoting axis therefor. Force means for applying force tending to move magnet 126 away from contacting relationship with conduit section 12 are provided in the structure shown by FIGURE in the form of spring 114 operativcly related to member 124 in a manner similar to the relationship of spring 114 to member 1168 discussed above in connection with PEG- URE 4.

A further modification of the temperature control struc ture shown by FIGURES 4 and 10 and discussed above is shown in FIGURE 11. The stated modification is adapted for use with workpieces of non-magnetic mate rials wherein no attraction of the material results regardless of the intensity of a magnetic field to which the material may be exposed. A segment or strip oi metal 149 is provided whereby magnet 126 on pivotally movable member 124 may be held in contact with strip by magnetic force as shown in FIGURE 11. Strip 14b is secured to arcuate bearing member 32 in housing portion 26 by suitable means such as one or more screws (not shown) and is adapted to contact the surface of a workpiece element such as conduit section 12 at the distal end of strip 14b in a bearing portion or tab 142. Thus, tab 142 will normally be at or very nearly at the same temperature as conduit section 12 by reason of its close and continuous contact therewith. The remaining structure of the modification shown by FIGURE 11 may be precisely the same as that discussed above in connection with FIGURES 4 or 10. Thus, member 1124 upon which magnet 126 is mounted may be pivotally supported between two bearing screws, one of which is indicated at 13th, with force means including spring guide 11% applying force at one end of member 124 as shown in FIG- URE 11.

Referring to FIGURES l2, 13, 14 and 15, means whereby power supply cables from units 2d and 22 may be connected to fixture 111- for brazing in remote locations is shown. The stated power connections include cables 1511 and 152 which may be joined by suitable means such as clamps or tapes 154 and 156. Since cables 15-11 and 152 are identical, only one need be described. Thus, cable 15d as shown by FIGURE 13, for example, includes an inner conductor 153 at the center thereof, and an outer conductor 1641 situated coaxially about conductor 158 and insulated therefrom by suitable dielectric material as shown at 162. Cables 15% and 152 further include an additional layer of insulating material as indicated at 164 in FIGURE 12 surrounding outer conductor 158 and separating the same from a metallic shield 166 coaxial with conductors 158 and 160. A suitable non-conducting and moisture-proof material is provided as an outer covering for cables 15% and 152 and is designated by reference numeral 168 in FIGURE 12. It will be understood by those skilled in the art that various other cable configurations, such as standard coaxial cable having only two conductors without a shield, might be used instead of cable 150 shown in FIGURE 13, for example. However, it is important to the inventive concept disclosed herein that the cables are not water cooled, since such cables are costly, heavy, relatively rigid and most unwieldy, hence not well suited for use with in-place brazing apparatus.

At the terminal end of cables 15% and 152 cooperatively related with brazing fixture 1t), plug means are provided to adapt the stated cable ends for connection with fixture 141. The stated connection means include two hollow tubular conductors 17d and 1'77. as seen, for example, in FIGURES 12 and 14, the distal ends of which are sized and beveled as indicated at 174 to form two plugs for connection within two spaced holes 176 and 1'78 in coil element fill adapted to receive the same. Hollow conductors 1% and 172 each function both as an electrical conductor and a fluid conduit. Thus, the end of each conductor opposite from the point of its connection with coil element 39 is connected to a hollow ilexible conduit ass and 182, respectively, wlereby a cooling agent such as air or other fluid may be supplied to hollow coils 46 in coil element 36 through conduits llilil, 1S2, conductors iitl, 172 and passages 48 and 5d discussed above.

it is of particular significance in the inventive concept disclosed herein that the cables connecting the power source with fixture id have very low resistance whereby the cable impedance matches the impedances of the brazing power generator-transformer combination. To this end, Where cables of the type shown in FIGURES 12-14 are used, inner conductors 158 and 159 in cables 152 and 15d, respectively, are positioned in close contact with conductor 17b and held against the same by an electrically conductive wrapping or clamp means as shown in FIGURE 13. The same wrapping or clamp means 134 is also positioned in intimate electrical contact around outer conductors res and 161 in cables 152. and respective ly, and contacts conductor 17% as also seen from FIGURE 13. Metallic shield and 16'? on cables 1% and 152, respectively, are each firmly contacted by a separate conductive wrapping or clamp means 186 which also contacts hollow conductor 1'72 as shown by FIGURE 12. From the stated relationship of parts, it will be understood that cables 15il and 152 are connected in parallel with each other, that conductors 1" 159, 16%, and 161 are electrically joined to conductor ll to form power input means for coil element fail, whereas metallic shield 1&6 and in cables 1% and 1523 are joined to conductor 172 to form the return power line and complete the circuit from input conductor 176i through induction coil element 30. A suitable dielectric material such as heat-resistant plastic may be molded or otherwise formed into an outer covering or plug member 187 as shown in FIGURES 12-14, with dielectric face plate 183 secured at the end thereof for bearing contact with surface 1% at the lower end or" coil element 3% shown, for example, in FIGURE 8.

It will be understood that when standard coaxial cable is used without a shield, the cable inner conductor may be connected to one tubular conductor such as 1711, while the cable outer conductor may be connected to the other tubular conductor 172 to complete the circuit between fixture 1d and the brazing power source. in using plain coaxial cable such as described in the foregoing arrangement, the cross-sectional area of the cable inner conductor should be approximately equal to the crosssectional area of the cable outer conductor.

A modification of the connection means shown by FIGURES 12-14 is shown by FEGURE 15 wherein conductors 17b and 1'72 terminate in female coupling means 192 and instead of the male coupling configuration shown by FIGURES l2 and 14. Thus, the connection means of FIGURE 15 is adapted for use with coil elements 35) having plug means of the general type shown at the distal end of conductors 17 ii and 172 in FIGURES 12 and 14. Except for the stated difference, it will be understood that the internal structure of FIGURE 15 may be identical to that described in connection with FEGURES 12-14.

As seen from the schematic showing of FIGURE 16, magnetic means in the form of lever 16 8 discussed above in connection with FIGURE 6, for example, is electrically related to the circuit by means of which power is applied to coils as in order to control the amount and duration of brazing heat. Thus, lever 1% is pivotally mounted at 111? whereby the left-end thereof as seen in FIGURE 16 contacts conduit section 1 due to magnetic force between the application of brazing heat. Secondary power means of low voltage, such as battery 1%, is provided to supply current through connection means 198 to a coil 200 in a relay generally designated by reference numeral 202 and thence through lever 108. Contact of lever 16% with conduit section 14 causes completion or" the electrical circuit through the stated conduit section by reason of connecting means 294 which electrically connect the conduit section with battery 196 to complete the switch circuit. It may also be seen from FIGURE 16 that the switch portion of relay 2th; is included in the power circuit connections between transformer 22 and coils 46 whereby operation of the relay may either interrupt or complete the stated circuit, either to prevent or to permit the application or" brazing heat.

Thus, it will be understood from the description of structure set forth above that closure of switch ass in connection 1% at the start of the brazin operation will apply power from battery 196 through relay 2&2 causing the relay to complete the power circuit whereby power from generator 2i) and transmitted through transformer 22 will cause induction coil as to apply brazing heat to sleeve or bushing 44. Application of heat in the manner stated will continue until the temperature of conduit section 44- reaches a value of temperature called the Curie point at which the material in conduit 14 loses its magnetic permeability and member 103 is no longer attracted to conduit section 14. When the stated change occurs, the magnetic force exerted by lever 1% on conduit 14 will no longer maintatin lever 1:38 in contact with the conduit section if any slight force is applied to the lever in a direction causing separation of the lever from the conduit surface. Force of the type described may. be applied either by a spring or by magnetic means acting on the end of lever 11% opposite from the end which contacts conduit section 14. Thus, for example, in FY- URE 16 a small magnet 2-bit is operatively positioned near the end of lever 1% whereby repelling magnetic force applied to the lever tends to cause rotation of the lever about pivot 11b in a clockwise direction. When the temperature of conduit section 14 reaches the Curie point whereby contact of lever 1% with the conduit surface is no longer maintained by magnetic att action therewith, the repelling force of magnet 2-bit acting upon leer 168 causes slight but sufiicient movement of the lever whereby electrical contact between lever 1% and conduit 14 is broken. When the stated interruption of the circuit from battery 1% occurs, power from the battery is no longer applied through relay 2592 and the relay automatically opens to interrupt the circuit bet-Ween transformer 22 and induction coil 46, thus causing termination of .power to the induction coil with consequent termination of the application of brazing heat.

Operation Although the apparatus disclosed herein may be used for automatic application of heat to a variety of diverse materials, workpieces, and for different purposes, its op eration need not in any case differ materially from that described below for the sake of illustration. Prior to use of the apparatus for brazing, a suitable brazing alloy is prepositioned under sleeve 44, and conduit sections 12 and 14 are aligned, with sleeve 44 over the abutting ends thereof.

With the workpiece components properly arranged as required, housing portion 24 of fixture 13 is positioned proximate the stated components as shown, for example, in FIGURES 2, 4 and 5. Quick and precise positioning of fixture 10 may be achieved by use of indexing means such as etched or inked mark 11 on conduit section 12 shown in FIGURE 2. Mark 11 is applied before installing fixture 10, and is located a measured distance from plane of abutment 42 whereby alignment of bearing member 78 with mark 11 will position fixture 10 so that pins 134 and 106 mounted thereon will center sleeve 44 precisely over the stated plane. Thus, even though the precise location of plane of abutment 49 is not visible, ac-

curate alignment of all workpiece components and of fixture lit in operative relationship therewith results from the teachings disclosed herein.

After positioning of annular housing portion 24 in the manner set forth above, annular housing portion 26 of fixture ltl containing coil element upper portion 32 as indicated in FIGURE 6, for example, is positioned in operative relationship with the assembled workpiece components by placing housing portion 26 in mating contact with portion 24, insuring that indexing stakes 23 and 25 enter holes 27 and 29 discussed above in connection with FIGURE 6. Due to the stated indexing means between housing portions 2 and 26, it may be seen that the position of annular housing portion 26 depends upon the position of portion 24-. The operative relationship of annular housing portions 24 and 26 described above is continuously maintained during the brazing operation by the action of studs 31, 33, 35 and 37 which extend between the stated housing portions and clamp the same together by means of holding nuts in the conventional and well known manner for such holding means.

After installing the several parts of fixture 10 as discussed above, lower portion 34 of coil element 36 may be assembled therewith by installing portion 34 in the space or opening 121i) provided on the lower or bottom surface of annular housing portion 24 as shown in F1 URE 6. Upon proper seating of portion 34 in operative relationship with upper coil portion 32, plug members 51 in each lower ring portion 4? will penetrate the hollow centers of each upper ring ortion 47 to complete rings 46 as discussed above in connection with FIGURE 9. Simultaneously, blade electrodes 55 and 57 attached to upper and lower ring portions 47 and 49, respectively, will engage each other by a wiping action during assembly of the two stated ring portions with each other. Following assembly of the components of fixture 1% as described above, alignment of coil element 30 within annular housing portions and 26 may be accomplished by adjustment screws 38 and 49 so that the position of induction heating rings 46 relative to brazing sleeve 44 will result in concentration of brazing heat at the proper location. When the stated alignment is comp ete, spring clamp means 36 on either side of fixture 24 may be pressed into engagement on either side of lower portion 34 of coil element 39 to maintain the esired position of adjustment and retain the coil element in operative relationship with the other components of fixture it as shown by FIGURE 2, for example.

Upon completion of the assembly procedures applicable to fixture it as described above, inert gas supply lines 96 and 93 may be connected to the fixture on either side thereof as shown by FIGURES 2 and 4, for example, and electrical connection between power source 20, transformer 22, and fixture it? may be accomplished as required and discussed above in connect-ion with FIG- URES 12-15, inclusive. Electrical connection is also made with pivotally movable member 168 to establish a low voltage circuit as shown schematically in FIGURE 16 to provide automatic temperature control means as referred to above.

Before application of brazing heat to the assembled workpiece components, a fiow of suitable inert gas such as argon is established through conduit means 96 and 98 whereby oxidation and other adverse effects on the workpiece components which might otherwise occur in the heated state are avoided. Thus, for example, argon gas may be introduced through conduits 9d and passage 1% thereby filling chamber 54 and exiting therefrom through passage 162 and conduit Flow of the inerting agent may be continuously maintained in the stated manner throughout the brazing operation. Since the inerting agent may be at a relatively low temperature, the stated purging procedure will afford the additional advantage of cooling conduit sections 12 and 14 in the areas thereof adjacent each end of sleeve 44, thus helping amass? ll to avoid annealing of the material in the stated area which otherwise might occur at the high temperatures associated With brazing in most materials.

With the apparatus connected as necessary to accomplish the brazing operation, switch 2% may be closed to actuate relay 2tl2 whereby radio frequency current flowing through coils as produces a high frequency magnetic field around the assembled workpiece components. It is this magnetic field oscillating at radio frequency that causes heating of the workpiece components by an action known as eddy current and hy teresis. In brazing workpiece components fabricated from 350 stainless steel together with standard silvernickel brazing alloy, induction heating near the plane of abutment 42 may produce a temperature close to 2000 F., whereas the temperature of conduit sections 12 and 14- in the area adjacent each end of sleeve will be much less, such as 1400-1500 F. Thus, when the temperature at the point of contact between pivotally movable member res and conduit section 12 reaches a value approximately 1350 F, magnetic attraction between the stated member and conduit section is lost due to the efiect referred to above as the Ourie point. When the stated loss of magnetic attraction occurs, the force of spring 1114- or of magnet 202i acting upon movable member 1% causes separating movement of the same whereby electrical contact is broken, causing interruption of the power circuit by operation of relay ZilZ, terminating the brazing cycle as discussed above.

From the description of structure and its operation as set forth above and shown in the drawings, it rncy be seen that the invention disclosed herein provides novel means for applying heat such as required for brazing operations in relatively remote and inaccessible areas. Fixture id is of extremely efi'icient and compact nature, and is readily adaptable for brazing a variety of different workpiece shapes and sizes, such as elbows, tees, crosses, reducers and many different kinds of bulkhead fittings. The feature which permits separation of fixture along a common plane and assembly thereof about an immovable and inaccessible workpiece provides great versatility in use of the fixture. Moreover, the purging means including arrangement of passages Nb and N2 and their relationship with chamber 54 provides new and useful results in producing a brazed joint of great strength and reliability, particularly by avoiding annealing aifects at either end of the brazing sleeve.

The ease of installation afforded by the various features described above makes possible the use of fixture lift for in-place brazing of various fluid lines and conduits, thus avoiding the necessity for disassembling and removing portions of structure from an aircraft, missile or other vehicle as required for bench brazing in a workshop. Thus, heat is concentrated at the precise location where brazing is accomplished, and is contained within a small local area whereby other lines or structural elements situated close to the brazing area are not affected by brazing heat. Moreover, the structural relationship between the mating portions of fixture ll il permitting separation of the same avoid the dangers of air leakage contacting the workpiece components and oxidizing the same, or electrical arcing across coil coupling 39 in rings 46. In addition, the relatively lightweight construction and arrangement of component parts in fixture ill results in rapid dissipation of brazing heat whereby the continued application of residual heat following the brazing operation does not produce widespread annealing of workpiece components, or consequent weakening of the brazed joint.

In addition to the novel features of fixture ill which adapt the same for in-piace brazing in relatively crowded structural areas, the cooperative relationship between cable 113 and fixture id permits use of the fixture in the stated manner. Thuncable is highly flexible, small in cross-sectional area and electrically very efficient whereby the cable delivers sufficient power to fixture id at distances fifty feet or more away from the power source. The problems normally associated with use of coaxial cable as a radio frequency conductor in brazing operations, such as the high percent of power loss in such cables and consequent longer heating cycle and greater area of annealment in the brazed workpieces, are avoided by the various features of construction for cable 1% and the coating provisions associated with coil element 30 in the instant case. Since the stated cooling provisions involve air, the larger diameter coaxial cable which would be necessary to provide the coolingtask for recirculating Water, for example, and consequent decrease in cable flexibility, are avoided by this invention. Due to the foreging cable characteristics, and the relationship between cable 18 and fixture it) as described above, inplace brazing to produce conduit connections. and the like having improved strength and structural reliability at locations remote from the brazing power source are achieved by the structure disclosed herein. In addition, automatic control of the brazing cycle whereby the application of brazing heat is accurately limited so that Workpiece components are heated to the liquidus temperature of the brazing alloy, and the further application of brazing heat is terminated, accomplishes further improvement in the characteristics of the brazed joint or connection produced by the structure disclosed herein.

It is of further significance in the inventive concept disclosed herein that coupling means 39 shown, for example, in FIGURE 9, and discussed above permits a suction or jet-purnp eifect at the connection of ring portions 47 and 49 whereby the region of contact between wall portions 58 and an externally thereof is continually evacuated during flow of cooling fluid through rings 4s. This feature may be enhanced by use of the alternative embodiment shown in FIGURE 8a, wherein cooling fluid supply lines 48 and 5t communicate with a common manifold or chamber 212. Chamber 212 communicates in turn with each of rings 4-6 through passages 214, whereby cooling fluid flows through the stated rings, exiting therefrom at apertures 52 as shown in FIGURE 8. During flow of cooling fluid through coupling means 39, it may be seen from FIGURE 9, for example, that upward flow through plug member 51 will produce suction of air through any spaces or gaps occurring between ring portion 4'7 and the upper half of plug 51 in the event that the contacting surfaces thereof do not fit snugly. When the manifold arrangement of FIGURE 8a is employed, plug members Sit may purposely be sized to fit somewhat loosely within ring portions 47, whereby the tendency for air or other cooling fluid under pressure to leak from coupling means 39 and to enter chamber 54 between the contacting surfaces of wall portions 58 and as is avoided.

While the particular details set forth above and in the drawings are fully capable of attaining the objects and providing the advantages herein stated, the structure and method thus disclosed are merely illustrative and could be varied or modified to produce the same results without departing from the scope of the inventive concept as defined in the appended claims.

We claim:

1. Induction heating means for causing heat in a localized area of a specimen, said means including housing means for supporting an induction heating element in stationary operative relationship with said area, said induction heating element comprising a tubular conductor, said housing means including a chamber enclosing said area, conduit means communicating with said chamber for supplying an inert gas to fill said chamber in conjunction with operation of said induction heating element, said conductor being constructed and arranged for support by said housing means externally of said chamber.

2. A method for brazing together a plurality of Workpiece components by inductively heating said components, including the steps of: placing said components in desired final relationship with a brazing material placed therebetween, placing around said components an enclosing chamber and an induction coil about said chamher and external thereof, flowing an inert gas at a relatively low temperature through said chamber, and energizing said coil to cause said heating while simultaneously during said heating continuing said gas flow at a rate sufiicient to lower the temperature Within said chamber.

3. Induction heating means for causing heat in a localized area of a specimen, said means including housing means for supporting an induction heating element in stationary operative relationship with said area, an induction heating element adjustably supported Within said housing means and movable with respect thereto, holding means for holding said induction heating element in continuous adjustment with respect to said housing means, said housing means further including a chamber enclosing said area, and conduit means communicating with said chamber for flowing a relatively low temperature inert gas through said chamber in conjunction with operation of said induction heating element.

4. The method of brazing a plurality of fluid conduit components installed in a fluid system comprising: applying heat to said components in an amount suificient to liquify a brazing alloy preplaced in the area to be brazed, sensing the magnetic permeability in the material of one of said components proximate the location Where said heat is applied, and automatically terminating the application of said heat when said magnetic permeability is lost.

References Cited in the file of this patent UNITED STATES PATENTS 

1. INDUCTION HEATING MEANS FOR CAUSING HEAT IN A LOCALIZED AREA OF A SPECIMEN, SAID MEANS INCLUDING HOUSING MEANS FOR SUPPORTING AN INDUCTION HEATING ELEMENT IN STATIONARY OPERATIVE RELATIONSHIP WITH SAID AREA, SAID INDUCTION HEATING ELEMENT COMPRISING A TUBULAR CONDUCTOR, SAID HOUSING MEANS INCLUDING A CHAMBER ENCLOSING SAID AREA, CONDUIT MEANS COMMUNICATING WITH SAID CHAMBER 